基于极化/去极化电流法的交联聚乙烯电缆热老化程度判定

Thermal Aging Status Diagnosis of XLPE Cable Using Polarization/Depolarization Current Method

准确诊断交联聚乙烯（XLPE）电缆的老化程度对于评估其绝缘状态有着重要的意义。为了得到不同老化程度的电缆样品,进行了人工加速热老化实验,老化温度为140℃,老化时间分别为10、20、30、40 d。同时,设计了可以去除表面电流干扰的电缆测量结构,以此测得了样品的体极化/去极化电流（PDC）,并用极化强度仿真验证了实验结果。不同的去极化曲线形状可以初步判断出电缆的老化程度,但不够直观。为了定量地描述电缆老化程度,采用了能够反映电介质内部陷阱的参数老化因子A,研究结果表明：随着老化程度增加,电缆的A值总体上呈现了上升的趋势;在140℃老化温度下,老化时间约为20~30 d时电缆进入中重度老化阶段。根据该实验结果建议针对运行时间约为15 a的电缆进行PDC绝缘老化检测。

Correctly diagnosing the aging status of cross-linked polyethylene （XLPE） power cable is very important for judging its insulation condition. In order to get XLPE cable samples with different aging status, artificial accelerated aging experiments（aging temperature is 140 ℃ and aging time is 10 d, 20 d, 30 d, 40 d） were carried out. We also designed a structure to eliminate the surface current and then measured the polarization/depolarization current of aging sample. Based on the measurement data, polarization intensity was calculated. The results show that different PDC curves can judge aging degree to some extent but not practical enough. To quantify the cable aging degree, the aging factor A, a pa- rameter describing the dielectric traps inside the XLPE, is adopted. The results show that A rises gradually with the increase of aging degree. Under 140 ℃ aging temperature, 20-30 day aging cable is in middle-heavy aging status. Con- sequently, it is suggested that a power company should carry out PDC test especially for 15 years-old cables.